ignore DetachCurrentThread calls for the main thread
ignore DetachCurrentThread calls for the main thread

My earlier commit to allow detaching the main thread (1f1c3c4) seems
to have caused subtle stability problems
(e.g. https://groups.google.com/group/avian/msg/d2c797c0dcf925c3), so
for now we'll just ignore that operation, which leaks a bit of memory
but should be harmless otherwise.

marcinolawski/avian,lwahlmeier/avian,bigfatbrowncat/avian-pack.avian,bigfatbrowncat/avian-pack.avian,getlantern/avian,marcinolawski/avian,minor-jason/avian,dicej/avian,marcinolawski/avian,bigfatbrowncat/avian-pack.avian,ucdseniordesign/avian,bgould/avian,MaartenR/avian,joshuawarner32/avian,dicej/avian,joshuawarner32/avian,lostdj/avian,bgould/avian,lostdj/avian,lwahlmeier/avian,joshuawarner32/avian,lostdj/avian,ucdseniordesign/avian,minor-jason/avian,MaartenR/avian,dicej/avian,dicej/avian,bigfatbrowncat/avian-pack.avian,getlantern/avian,ucdseniordesign/avian,lwahlmeier/avian,MaartenR/avian,MaartenR/avian,getlantern/avian,getlantern/avian,joshuawarner32/avian,lwahlmeier/avian,ucdseniordesign/avian,marcinolawski/avian,bgould/avian,minor-jason/avian,lostdj/avian,bgould/avian,minor-jason/avian